Ace honda — Regarding the service problem

Sir, I have baught a Honda city car from Ace Honda sector -11, Noida in June 2015 . My car is serviced regularly at Ace Honda service centre on time . Whole purchasing this car, I have taken the extended warranty, now after 18 months of buying this vehicle the battery is not working and the Ace Honda service centre authorities is saying the battery is dead . As the car is serviced on time regularly by the concerned service centre how can the battery is damaged in a short time . Now they are not listening to my problem . They are totally different from the time of sales